For a multi-tenant and hybrid security approach, which recommendation is most suitable?

In a multi-tenant and hybrid security approach, Azure AD B2C is particularly suitable due to its focus on identity management tailored for multi-tenant applications. Azure AD B2C (Business to Consumer) allows organizations to manage their user identities and provide secure access to applications across various platforms. It is designed to handle multiple tenants seamlessly, which means that organizations can offer their applications to different customer segments without compromising security or usability.

Azure AD B2C supports hybrid scenarios by allowing the integration of both local identities and social identities from various sources, ensuring that users have a flexible and secure experience. This fits well in environments where organizations need to cater to numerous users who may be accessing resources from different places, including cloud and on-premises solutions.

The other options, while valuable in different contexts, are not specifically aimed at providing a multi-tenant and hybrid identity management solution. Azure Arc primarily focuses on extending Azure management to on-premises and other cloud environments, Microsoft 365 Defender is centered around threat protection across Microsoft 365 services, and Azure Firewall acts as a network security resource rather than an identity management tool. Hence, Azure AD B2C emerges as the most fitting recommendation for managing multi-tenant and hybrid security effectively.